<!DOCTYPE html>
<html>
<head>
	<meta charset="utf-8">
	<title>children</title>
</head>
<body>
	<ul id="ul1">
		<li></li>
		<li></li>
		<li></li>
	</ul>
	<script>
		window.onload = function(){

		var oUl = document.getElementById("ul1")
		alert(oUl.children.length)
		}
	</script>
	
</body>
</html>